Emergence of a molecular quantum liquid in one dimension

TL;DR

This paper explores how a one-dimensional lattice of hard-core bosons with attractive interactions forms a molecular quantum liquid, revealing emergent phases like phase separation and charge order through advanced numerical and theoretical analysis.

Contribution

It uncovers the emergence of a molecular quantum liquid and phase-separated states driven by virtual quantum fluctuations in a strongly interacting 1D system.

Findings

Formation of dimerized molecules at large attraction

Emergence of phase separation and charge-density wave puddles

Charge order sensitivity to unpaired atoms

Abstract

We investigate the fate of a one-dimensional lattice superfluid formed by hard-core bosons, aka `atoms' (alternatively, a free spinless Fermi sea) subjected to nearest-neighbor attractive Hubbard-like interactions only in subgroups of two sites. The system, as expected, stabilizes a fluid of dimerized molecules at large attractive interactions. However, the composite molecules have an effective meek hopping scale and dominant repulsive interactions solely due to virtual quantum fluctuations. Interestingly, at an intermediate attractive potential, the system realizes a phase-separated region where the system is in an absorbing state. We show that this phase-separated region is due to an emergent attractive interaction between the dimers which leads to a local charge-density wave puddle where particles effectively cluster with local half-filling. Moreover the molecular superfluid gets spontaneously charge-ordered in the addition of an unpaired atom, reflecting the extreme sensitivity of the system to the existence of lone atoms. Using density-matrix renormalization group studies and effective low-energy Hamiltonians, we isolate the quantum processes to uncover the physics behind molecule formation in a strongly interacting one-dimensional system.